The long-term goal of the proposed research is to determine the structure of the component(s) in human transfer factor (TF) responsible for systemic transfer of donor-specific, dermal reactivity in man. Our work over the last three years has established reproducible methods for preparing and testing (systemic transfer in man) large, multi-unit batches of TF from immunized donors. Using these methods, we have established that (a) TF to a selected antigen (KLH) is only apparent after immunization, (b) TF can be purified by gel filtration, isoelectric focusing (IEF), and reverse phase, high pressure liquid chromatography (HPLC), (c) the purified TF is not inactivated by alkaline phosphatase although its fractionation characteristics on IEF and HPLC are changed, (d) TF is susceptible to pronase and this susceptibility is blocked by a specific pronase inhibitor (traysylol). These and other properties allow us to propose a model structure (5'-Inosine-oligopeptide) for TF. This proposal details experiments to confirm and to elucidate further the structure of human TF. The experiments include additional purification, enzymatic and chemical probes, structural determinations, and complete analysis of specificity. The reproducibility of the systemic transfer system with KLH markers makes it possible to conduct these experiments in a reliable manner. The structural definition of TF should provide clues to the underlying biologic mechanism of the transfer phenomenon and provide defined reagents for clinical trials.